In 1997, Congress cracked down on a popular tax shelter that allowed rich people to take advantage of the exempt status of charities without actually giving away much money.
Individuals who had already set up these vehicles were allowed to keep them. That included Mitt Romney, then the chief executive officer of Bain Capital, who had just established such an arrangement in June 1996.
Go read the whole thing. Here's the gist: For years now, Romney has basically been renting the tax-exempt status from his church.